Use of an amphoteric surfactant as a friction-reducing agent

ABSTRACT

An alkoxylated alkanolamide of general formula (I), ##STR1## wherein R is a hydrocarbon group having 7-35 carbon atoms, preferably 9-23 carbon atoms, A is an alkyleneoxy group having 2-4 carbon atoms, and n is 2-20, preferably 3-12, is used for producing a water-based liquid system with reduced flow resistance between the flowing, water-base liquid system and a solid surface.

The present invention relates to the use of an amphoteric surfactant ina water-base system for reducing the flow resistance between a solidsurface and the water-base liquid system.

It is well-known that the flow resistance of a liquid in a conduit islargely due to the turbulence that arises at the conduit wall.Surfactants with the ability to form extremely long, cylindricalmicelles have, in recent years, attracted a great interest asfriction-reducing additives to systems with circulating water,especially those destined for heat distribution. An important reason forthis interest is that, although one desires to maintain a laminar flowin the conduits, one wishes at the same time to have turbulence in theheat exchangers to achieve therein a high heat transfer per unit area.

The rod-shaped micelles are distinguished by operating in a fairlydisorderly fashion at low Reynold's numbers (below 10⁴), and having noor only a very slight effect on the flow resistance. At higher Reynold'snumbers (above 10⁴), the micelles are paralleled and result in afriction reduction very close to that which is theoretically possible.At even higher Reynold's numbers (e.g. above 10⁵), the shear forces inthe liquid become so high that the micelles start to get torn and thefriction-reducing effect rapidly decreases as the Reynold's numbersincrease.

The range of Reynold's numbers within which the surface-active agentshave a maximum friction-reducing effect is among others dependent on theconcentration, the range increasing with the concentration.

By choosing the right concentration of surface-active agents andsuitable flow rates in tubings and heat exchangers, it is thus possibleto establish a laminar flow in the tubes and turbulence in the heatexchangers. Thus, the dimensions of both the tubes and the exchangerscan be kept at a low level, or the number of pump stations, andconsequently the pump work, can alternatively be reduced while retainingthe same tubular dimensions.

Most of the surface-active agents hitherto used as friction-reducingadditives to circulating water system--mainly destined for heatdistribution, see for example WO 85/03083--are cationic surfactants likeC-₁₆₋₁₈ -alkyltrimetyl ammonium salicylate. However, this type ofsurface-active agent is slowly degraded, both aerobically andanaerobically, and is highly toxic to marine organisms. Sinceheat-distribution systems usually suffer from important leaks (it isestimated that in one year 60-100% of the water leaks out), it followsthat the added chemicals end up in the ground water and in variousfresh-water recipients. This combination of low biodegradability andhigh toxicity is a fundamental criterion for a product injurious to theenvironment.

In the Swedish Patent publication No 467 826 it is disclosed thatnonionic, alkoxylated alkanolamides may be used as friction-reducingagents. These nonionic surfactants have an excellent friction reducingeffect at low or moderate temperatures but at higher temperatures thefriction reducing effect is less satisfactory and may even be lost.

It has now surprisingly been found that a water-soluble amphotericsurfactant containing

i) one or more, preferably one or two, monovalent hydrophobic groups,preferably hydrocarbon groups, forming a hydrophobic portion containing10-36 carbon atoms,

ii) one or more, preferably one or two primary, secondary or tertiaryamine groups and

iii) one or more, preferably one or two carboxylic groups and having amolecular weight of less than 1400, preferably less than 800, or a saltthereof has the ability to form long cylindrical micelles. Theamphoteric surfactant may also contain one or more nonionic, hydrophilicgroups, such as hydroxyl groups and ether groups. This type ofamphoteric surfactant has an excellent friction-reducing effect welladapted for aqueous heat transfer systems. Furthermore, the effect ofthe amphoteric surfactant on the environment is low, especially incomparison with the previous used cationic friction-reducing agents. Theamount of the amphoteric friction-reducing agent may vary within widelimits depending on the conditions but generally is 100-10.000 g/m³ ofthe aqueous heat transfer liquid.

Suitable amphoteric surfactants to be used as friction-reducing agentsare those surfactants which have the formula ##STR2## where R₁, R₃, R₄and R₅ independently are carboxyalkyl groups with 2-22, preferably 2-4carbon atoms or dicarboxyalkyl groups with 3-22, preferably 3-4 carbonatoms, or the group

    R (OC.sub.r H.sub.2r).sub.p A.sub.q (OC.sub.s H.sub.2s).sub.n !.sub.v(II)

where R is hydrogen or an hydrocarbon group with 1-22 carbon atoms, A is--OCH₂ CH(OH)CH₂ --, --C(O)-- or --CH(OH)CH₂ --, r and s are numbersfrom 2-4, p and n are numbers from 0-10, v is a number 0 or 1, and q isa number 0 or 1, with the proviso that p is 0 when A is --CH(OH)CH₂ --,and p and n are both zero when A is --C(O)--, at least one of R₁, R₃, R₄and R₅ being the dicarboxyalkyl or carboxyalkyl group and at least oneof R₁, R₃, R₄ and R₅ being the group with formula (II) having an R groupwith 8-22, preferably 10-18 carbon atoms, the total number of carbonatoms in all R groups being 8-36, preferably 10-32 carbon atoms; R₂being an alkylene group with 2-3 carbon atoms and u is a number from0-3, preferably 0-1.

One preferred group of compounds with formula (I) are those with theformula ##STR3## where one or two of R₁, R₃ and R₄ independently arecarboxyalkyl with 2-22, preferably 2-4 carbon atoms or dicarboxylicgroups with 3-22, preferably 3-4 carbon atoms and one or two of R₁, R₃and R₄ independently are the group

    R (OC.sub.r H.sub.2r).sub.p A.sub.q (OC.sub.s H.sub.2s).sub.n !.sub.v (IV)

where R, r, p, A q, s, n and v have the meaning mentioned above, atleast one of R₁, R₃ and R₄ being a group with formula (IV) having an Rgroup with 8-20, preferably 10-18 carbon atoms, the total number ofcarbon atoms in all R groups being 8-36, preferably 10-32. Preferably, qis 1 and s and n are 0.

In formulae (II) and (IV) the R-groups are preferably an aliphaticgroup. Examples of suitable acyclic groups are octyl, decyl, dodecyl,hexadecyl and octadecyl. In case R is an alkylaryl group likeoctylphenyl, nonylphenyl or dodecylphenyl, then p is preferably 1-5 andA the group --OCH₂ CH(OH)CH₂ --. The groups --OC_(r) H_(2r) -- and--OC_(s) H_(2s) -- are preferably oxyethylene groups. Especiallyadvantages friction reducing effects have been shown byN-(2-hydroxyalkyl)sarcosinates where the alkyl group is saturated orunsaturated, branched or unbranched and contains 16-20 carbon atoms.

The friction-reducing effect of the surfactants according to theinvention is affected of both the temperature and the pH-value of thesolution. The temperature effect depends on wether the surfactantcontains glycol ether groups, or not. If no such groups are present, thesurfactant will be more hydrophilic with increasing temperature. Thepresence of glycol ether groups will affect the surfactant to be morehydrophobic when the temperature is increasing. The relative amount ofthe glycol ether groups to the ionic groups i.e. the amino andcarboxylic groups will thus determine wether the surfactant will be morehydrophilic or hydrophobic when the temperature is changed.

The balance between the hydrophilic and hydrophobic parts of thesurfactant is important for its function as a friction-reducingadditive. By using a proper balance between the number of ionic groupsand nonionic groups it is possible to design amphoteric surfactants witha small temperature dependence which then can be used as frictionreducing agents within a wide temperature range.

The hydrophilicity of the amphoteric surfactants according to thisinvention is also affected by the pH-value of the water-base liquidsystem. Within the pH-range of 5-11 an increase of the pH will increasethe hydrophilicity of the ionic groups and due to that thefriction-reducing properties of the amphoteric surfactant are affected.This is of importance because the amphoteric surfactant can be adjustedto give optimal performance within a certain temperature range by anaddition of an acid or a base. Also contaminations with an influence onthe surfactants micellar shape, such as hydrocarbons or higher alcohols,may be compensated for by an adjustment of the pH-value.

The aqueous heat transfer system contains at least 50%, preferably atleast 90% by weight of water. Apart from the amphoteric surfactant itmay also contain a number of conventional components such ascorrosion-preventing agent, anti-freeze, bactericides and solubilizers.

The amphoteric compounds with formula (I) may be produced in a number ofways. The following Examples illustrate some of the most conventionalmethods. In the formulae R, R₄ and p have the meaning mentioned earlier.

1. A higher alkyl amine is added to the Na-salt of fumaric acid ##STR4##2. A dialkylamine is added to acrylic acid ethyl ester ##STR5## 3. Ahigher alkane-1,2-epoxide is added to sarcosine: ##STR6## 4. A higheralcohol is first ethoxylated with p moles of ethylene oxide per molealcohol and to this product is one mole epichlorohydrin added withtin(IV)chloride as catalyst: ##STR7## The product II is then treatedwith alkali to give the corresponding epoxide: ##STR8## Two moles ofthis epoxide III are then added to one mole of glycine: ##STR9## 5. Anα-halogenated carboxylic acid is treated with ammonia or a primary orsecondary alkylamine to give the wanted amphoteric compound: ##STR10##6. One mol of a fatty alkyl dipropylenetriamine is reacted with one moleof the compound CH₂ ═CHCOOC₂ H₅, in order to carboxyethylate one of theamino groups. The ester group is then hydrolysed with alkali.

The present invention is further illustrated by the following Examples.

EXAMPLE

Measurements were carried out in a 6-m tube loop consisting of twostraight and stainless tubes (3 m each), one tube having an innerdiameter of 8 mm and the other having an inner diameter of 10 mm. Waterwas pumped through the tube loop by a centrifugal pump, which was drivenby a frequency-controlled motor, for continuous adjustment of the flowrate, which was determined by a rotameter.

The straight parts of the tube loop had outlets which, with the aid ofvalves, could in turn be connected to a differential pressure gaugewhose other side was all the time connected to a reference point in thetube loop. Further, the tube loop was heat-insulated, and the suctionside of the pump was connected to a thermostatically controlledcontainer with a volume of 20 l, to which the return flow from the tubeloop was directed.

After the testing compound had been added and the aqueous solution hadbeen thermostatically controlled, measurements began at low flow rates,and the pressure difference from two points on the 10-mm tube and threepoints on the 8-mm tube were measured for each flow rate. The pressuredifferences thus measured were then converted into Moody's frictionfactor Y and are shown in the Table below as a function of the Reynold'snumber Re.

Y=2D.P_(diff) /V².L.d

Re=D.V.d/u

D=tube diameter

V=flow rate

L=tube length over which the pressure difference P_(diff) was measured

d=density of the liquid

u=viscosity of the liquid

The Table also states the corresponding Prandtl number and Virk number.The former corresponds to the friction factor of water only, i.e. withturbulence, and the latter corresponds to flow without turbulence.

In the tests performed one of the following compounds was added as afriction-reducing agent.

A. Cetyl trimetyl ammonium salicylate (comparison compound)

B. N-(2-hydroxy-cetyl)sarcosinate

C. N-(glyceryl myristyl ether)sarcosinate

D. N-cetyl sarcosinate

E. N-(2-hydroxystearyl)sarcosinate

F. N-C₁₆₋₁₈ -alkyl iminodipropionate

                  TABLE 1                                                         ______________________________________                                        Compound A, addition 1000 ppm, temperature 50° C.                                 Moody's friction factor × 10.sup.3                           Reynold's number × 10.sup.-4                                                         1       2      4      6    8                                     ______________________________________                                        Prandtl number × 10.sup.3                                                            30      24     22     21   20                                    10 mm        35      15     8.0    6.0  17                                    8 mm         30      12     6.0    6.0  18                                    Virk number × 10.sup.3                                                               11      7.2    5.2    4.3  3.9                                   ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Compound B, addition 500 ppm, temperature 66° C., pH-value 8.5                    Moody's friction factor × 10.sup.3                           Reynold's number × 10.sup.-4                                                         1       2      4      6    8                                     ______________________________________                                        Prandtl number × 10.sup.3                                                            31      27     22     20   19                                    10 mm        23      12     4.6    19   19                                    8 mm         22      12     9.5    20   19                                    Virk number × 10.sup.3                                                               11      7.2    5.2    4.3  3.9                                   ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Compound B, addition 500 ppm, temperature 98° C., pH value 8.2         Reynold's number ×                                                                   Moody's friction factor × 10.sup.3                         10.sup.-4    0.8    1.5   2.3  3.0 3.8  5.4 6.9  9.1                          ______________________________________                                        Prandtl number × 10.sup.3                                                            33     28    25   24  22   20  19   18                           10 mm        29     14    7    5   4    5   12   15                           8 mm         14     8     6    6   7    15  18   18                           Virk number × 10.sup.3                                                               13     9     7    6   5    5   4    4                            ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Compound C, addition 2000 ppm, temperature 35° C., pH value 7.4                     Moody's friction factor × 10.sup.3                         Reynold's number × 10.sup.-4                                                           0.4     0.6   0.8   1   2                                      ______________________________________                                        Prandtl number × 10.sup.3                                                              40      37    33    31  27                                     10 mm          28      18    17    13  27                                     8 mm           38      30    23    31  27                                     Virk number × 10.sup.3                                                                 20      17    13    11  7.2                                    ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Compound B, addition 1000 ppm, temperature 60° C., pH 9.0              Reynold's number ×                                                                  Moody's friction factor × 10.sup.3                          10.sup.-4   1.15    1.4    1.7  1.9  2.1  2.4  2.9                            ______________________________________                                        Prandtl number × 10.sup.3                                                           30      28     27   26   25   25   24                             10 mm       15      16     17   14   12   12   12                             8 mm        23      18     15   12   11   9    15                             Virk number × 10.sup.3                                                              10      9      8    7    7    7    6                              ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Compound E, addition 400 ppm, temperature 95° C., pH 9.0               Reynolds number ×                                                                    Moody's friction factor × 10.sup.3                         10.sup.-4    1.1    1.5   1.8  2.2 2.5  2.9 3.3  3.6                          ______________________________________                                        Prandtl number × 10.sup.3                                                            31     28    27   25  24   24  23   23                           10 mm        21     8     8    10  7    8   9    21                           8 mm         15     16    12   8   7    10  17   22                           Virk number × 10.sup.3                                                               11     9     8    7   7    6   6    5.5                          ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Compound A, addition 400 ppm, temperature 70° C.                                    Moody's friction factor × 10.sup.3                         Reynold's number × 10.sup.-4                                                           1.1   1.9     2.5 3.4   5.0 7.7                                ______________________________________                                        Prandtl number × 10.sup.3                                                              31    27      24  23    20  19                                 10 mm          60    34      30  25    20  18                                 8 mm           44    29      26  24    20  18                                 Virk number × 10.sup.3                                                                 11    8       7   6     5   4                                  ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Compound F, addition 1000 ppm, temperature 51° C., pH 5.4              Reynold's number ×                                                                  Moody's friction factor × 10.sup.3                          10.sup.-4   0.83   1.03   1.24 1.45 1.65 1.86 2.07                            ______________________________________                                        Prandtl number ×                                                                    31     30     29   28   27   26   26                              10.sup.3                                                                      10 mm       19     24     19   19   27   28   27                              8 mm        25     17     12   14   14   16   28                              Virk number × 10.sup.3                                                              12     11     10   9    8    8    7                               ______________________________________                                    

From the results it is evident that the friction reducing agent inaccordance with the invention essentially reduces the friction. In manycases the friction is reduced down towards the theoretical frictionlevel of laminar flow (the Virk line). The improvements in comparisonwith the prior art (table 1 and 7) is of considerable magnitude attemperatures commonly used in aqueous heat distribution system. From theTables 2, 3, 5 and 6 it is shown that according to the inventionfriction reducing agents have an excellent effect in the temperatureinterval from 60° to 98° C., while the comparison compound A has no oronly a very low friction reducing effect at 70° C. (Table 7).

We claim:
 1. A method for reducing the flow resistance between a solidsurface and a water-based liquid system which comprises adding to saidsystem a water soluble amphoteric surfactant having a molecular weightof less than 1400, or a salt thereof, wherein said amphoteric surfactantcontains one or more monovalent hydrophobic groups forming a hydrophobicportion containing 10-36 carbon atoms; one or more primary, secondary ortertiary amine groups; and one or more carboxylic groups.
 2. The methodof claim 1 wherein the amphoteric surfactant has a molecular weight ofless than 800 and contains one or two hydrocarbon groups containingtogether 12-22 carbon atoms.
 3. The method of claim 1 wherein theamphoteric surfactant contains one or more nonionic, hydrophilic groups.4. The method of claim 1 wherein the amphoteric surfactant has theformula ##STR11## wherein R₁, R₃, R₄ and R₅ independently arecarboxyalkyl groups with 2-22 carbon atoms or dicarboxyalkyl groups with3-22 carbon atoms, or the group

    R (OC.sub.r H.sub.2r).sub.p A.sub.q (OC.sub.s H.sub.2s).sub.n !.sub.v(II)

wherein R is hydrogen or an hydrocarbon group with 1-22 carbon atoms, Ais --OCH₂ CH(OH)CH₂ --, --C(O)--, or --CH(OH)CH₂ --, r and s are numbersfrom 2-4, p and n are numbers from 0-10, v is a number 0 or 1 and q is anumber 0 or 1 with the proviso that p is 0 when A is --CH(OH)CH₂ -- andp and n are both zero when A is --C(O)--, at least one of R₁, R₃, R₄ andR₅ is a dicarboxyalkyl or carboxyalkyl group and at least one of R₁, R₃,R₄ and R₅ is a group of the formula (II) having an R group with 8-22carbon atoms, wherein the total number of carbon atoms is in all Rgroups being 8-36 carbon atoms; and R₂ is an alkylene group with 2-3carbon atoms and u is a number from 0-3.
 5. The method of claim 4wherein the amphoteric surfactant has the formula ##STR12## where one ortwo of R₁, R₃ and R₄ independently are carboxyalkyl with 2-4 carbonatoms or dicarboxyalkyl groups with 3-4 carbon atoms and one or two ofR₁, R₃, and R₄ independently are the group

    R (OC.sub.r H.sub.2r).sub.p A.sub.q (OC.sub.s H.sub.2s).sub.n !.sub.v(IV)

where R, r, p, A, q, s, n and v have the meanings mentioned above, atleast one of R₁, R₃ and R₄ is a group of the formula (IV) having an Rgroup with 10-18 carbon atoms, wherein the total number or carbon atomsin all R groups being 10-32.
 6. The method of claim 5 wherein R is analiphatic group, q is 1 and n is
 0. 7. The method of claim 1 wherein theamphoteric surfactant is used in an amount of 100-10,000 g/m³ of thewater-base liquid system.
 8. The method of claim 1 wherein thewater-based liquid system is a heat transfer system.
 9. The method ofclaim 8 wherein the temperature in the system is in the range of atleast from 60° and 100° C.